<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <div>Ctrl+Shift+F</div>
    <div>Ctrl+S</div>
    <div id="app" style="width: 500px;height: 200px;background-color: #cecece;">
        <textarea></textarea> 
    </div>
    <script>
        var Ctrl_S = function (e) {
            if (e.ctrlKey == true && e.keyCode == 83) {
                alert("Ctrl_S");
                //阻止事件冒泡
                e.stopPropagation();
                e.preventDefault();
                return false;
            }
        };
        document.addEventListener("keydown", Ctrl_S, true);
        var Ctrl_Shift_F = function (e) {
            if (e.shiftKey == true && e.altKey == true && e.keyCode == 70) {
                alert("Ctrl_Shift_F");
                //阻止事件冒泡
                // e.stopPropagation();
                e.preventDefault();
                return false;
            }
        };
        document.getElementById("app").addEventListener("keydown", Ctrl_Shift_F, false); 
    </script>
</body>

</html>